This project aims to understand various cell activities that involve structural changes in supramolecular biomolecular complexes. Recent emphasis has been on developing mathematical and physical tools to investigate mechanisms involved in biological vesicle formation. For example, to understand the role that coat proteins can play in receptor mediated endocytosis, we developed an energetic model of clathrin basket assembly and, by analyzing data on size distributions of reconstituted basket, we estimated energies associated with changes in local clathrin lattice structure. We thereby confirmed that clathrin lattice formation can occur by passive, pair-wise insertions and deletions in the interior of existing lattice patches. Other studies involved elastic deformation analysis of clathrin triskelia, which showed that the rigidity of a clathrin patch is comparable to that of a typical plasma membrane. We continued our use of fluorescence recovery after photobleaching (FRAP) to examine phase changes that occur in cellular lipid membranes maintained at temperatures near their growth temperatures. Several projects involving tubulin and other polymers also were undertaken: a unique ultra-small angle x-ray scattering (USAXS) spectrometer, located at Argonne National Laboratory, was used to study supramolecular aggregates of tubulin rings induced by various marine natural products; an inelastic neutron scattering instrument at the National Institute of Standards and Technology (NIST) was used to examine the effects of polymerization on the vibration spectrum of associating macromolecules (fibrinogen); construction was started of a fluorescence correlation microscope (FCM) that will be used in our laboratory to examine dynamic events occurring at cell surfaces; mathematical analysis of phosphatidylinositide polyphosphate metabolic cycles was carried out to understand how such molecules might be involved in triggering endocytosis and other cellular events.Jin AJ, Nossal R. Rigidity of triskelion arms and clathrin nets. Biophys J 2000;78:183-1194.Watts NR, Sackett DL, Ward RD, Miller MW, Wingfield PT, Stahl SS, Steven AC. HIV-1 rev depolymerizes microtubules to form stable bilayered rings. J Cell Biol 2000;150:349-60.